This invention relates in general to an apparatus and methods for controlling the administration of radiation to a patient, and more particularly, to stereotactically directed radiation apparatus and radiation therapy and surgery performed by the apparatus.
The use of a computerized tomographic (CT) scanner or a Magnetic Resonance Imaging (MRI) system has been generally used to aid in diagnostic procedures or to aid in planning placement of a patient prior to the patient receiving radiation. The patient was then removed from the CT or MRI unit and radiation therapy was performed on a secondary system physically removed from the scanning facility. The employment of a second apparatus was due to the fact that the radiation levels necessary for radiation therapy were incompatible with the levels required for diagnostic procedures. The secondary radiation (scatter) from the treatment system required that it be placed in a separate, shielded room. Attempting to successfully reposition the patient in the secondary device, along with potential physiological changes which may occur in the=patient, can cause considerable problems in insuring a successful outcome with minimal danger to the patient.
Radiation therapy has generally been practiced utilizing either a Cobalt 60 radioactive source (1.2 MeV energy) or a linear accelerator with electron energies ranging typically from 4.0 to 20 MeV. Most existing radiation therapy technology provides radiation from a single focal point. Custom shielding blocks, and beam shapers are necessarily utilized in most treatments to deliver a uniform dose to the target without overdosing the surrounding area of healthy tissue. The radiation field size which is emitted from the device is typically controlled through movable collimators. This type of system has several severe limitations; the dose delivered to the area surrounding the target site receives as much or more radiation as the target itself. The limiting factor in treating tumors in many instances is the radiobiological effect, e.g., tissue damage, which may be delivered to the surrounding healthy tissue. In many cases, radiation therapy will be more effective if higher doses of radiation can be directed to the target site without subjecting the surrounding area to toxic amounts of radiation. Current practice typically incorporates laser positioning systems to determine patient location prior to treatment. This positioning is confirmed and recorded by placing a tattoo on the patients skin. The accuracy of this procedure requires that a treatment "margin" be included to compensate for the following types of factors: a) mislocation of a patient; b) growth of the target during the treatment program(which may take up to six weeks); and c) physiological movement of the position of the target between treatments (several days can elapse between treatments). Also, in treatments to date patients are administered radiation in a static modality, and the patient is not moved during the administration of radiation during treatment.
Current technology for therapy systems requires that external shielding, typically 24-60 inches of reinforced concrete, be utilized to prevent generalized exposure to the scattered radiation present in the treatment room. The requirement for this shielding has restricted treatment rooms to locations in facilities which can support the resulting high floor weight loadings.